Vol. I · A Postgres HandbookTwelve chapters · · 756 queries

The Query & the Schema

A reading-room reference for writing PostgreSQL by hand — selects to window functions, with the schema in plain view.

IntermediatePerformance & Indexes

Create a UNIQUE index

SQL

CREATE UNIQUE INDEX idx_unique_ssn 
ON employees (ssn);

Tested against PostgreSQL 16

Note

“Functions identically to a UNIQUE constraint but is explicitly created as an index. Prevents duplicate values.